[llvm] r212638 - AArch64: Better codegen for storing to __fp16.

[Tim Northover]

> Absolutely.  Greedily fusing double -> float -> __fp16 is correct with higher frequency than the old state of affairs, given the current front-end.

I don't think that makes it the right thing to do though. We've
replaced 1 bug with 2 that just happen to cancel out most of the time.

Feel free to assign the bug to me. I actually quite like
IEEE-conformance stuff. Gives the pedant in me free reign, which is
always refreshing. (And it'll give me a chance to fix InstCombine,
which gets it wrong now).

Tim.